As polarizers (also referred to as polarization splitters) used for image display devices, such as liquid crystal display devices, rear-projection televisions and front projectors, and showing a polarization separation ability in a visible light region, there are absorptive polarizers and reflective polarizers.
An absorptive polarizer is, for example, a polarizer having a dichroic dye, such as iodine, aligned in a resin film. Such an absorptive polarizer has a low light use efficiency because of absorbing one of polarized light waves.
On the other hand, a reflective polarizer has a higher light use efficiency since light that has been reflected without entering the polarizer is allowed to enter. For this reason, a demand for such a reflective polarizer is growing for the purpose of increasing the luminance of e.g. liquid crystal display devices.
A reflection polarizer is classified into a linear polarizer composed of laminated, birefringent resin films, a circular polarizer composed of a cholesteric liquid crystal, and a wire-grid polarizer.
Such a linear polarizer and a circular polarizer have a low polarization separation ability. For this reason, such a wire-grid polarizer showing a high polarization separation ability attracts attention.
A wire-grid polarizer is configured to have a plurality of fine metallic wires disposed in parallel to one another on a light-transmitting substrate. When the pitch between of adjacent fine metallic wires is sufficiently shorter than the wavelength of incident light, a component in the incident light that has an electric field vector perpendicular to the fine metallic wires (i.e. p-polarized light) is transmitted, while a component in the incident light that has an electric field vector in parallel to the fine metallic wires (i.e. s-polarized light) is reflected.
As wire-grid polarizers showing a polarization separation ability in the visible light region, the following types are known.
(1) A wire-grid polarizer having fine metallic wires disposed at certain pitches on a light-transmitting substrate (Patent Document 1)
(2) A wire-grid polarizer having a plurality of ridges formed at certain pitches on a light-transmitting substrate, the ridges having a top face and lateral faces covered with a material film of metal or a metal compound to form fine metallic wires (Patent Document 2)
(3) A wire-grid polarizer having a plurality of ridges formed at certain pitches on a light-transmitting substrate, the ridges having a metal layer disposed thereon to form fine metallic wires (FIG. 3 of Patent Document 3)
(4) A wire-grid polarizer having a plurality of ridges formed at certain pitches on a light-transmitting substrate, the ridges having a metal plate member disposed thereon to form fine metallic wires (Patent Document 4)
Among them, the wire-grid polarizer in item (1) has a low productivity since the fine metallic wires are disposed by lithography.
The wire-grid polarizers in items (2), (3) and (4) have a low polarization separation ability since the fine metallic wires are disposed on only the ridges. The optical properties vary depending on the angle or wavelength of incident light.